Socket Size Chart: Complete Guide

When working with nuts, bolts, and fasteners, one of the most essential tools you’ll need is a socket set. Sockets save time, increase precision, and help you tighten or loosen bolts without damaging them. But here’s the challenge—fasteners come in all kinds of sizes, and sockets are designed to match them exactly. That’s why a socket size chart is so important.

Whether you are a professional mechanic, DIY enthusiast, or someone who just wants to fix things around the house, understanding socket sizes will make your job smoother and more efficient. In this complete guide, we’ll explore what sockets are, how to read a socket size chart, the difference between metric and SAE sizes, drive sizes, and tips for choosing the right socket for your task.

What Is a Socket?

A socket is a tool that fits over the head of a bolt or nut, allowing you to apply torque using a ratchet or wrench. Unlike open-ended wrenches, sockets grip the entire head of the fastener, which prevents slipping and reduces the risk of rounding the corners.

Sockets are available in different:

• Sizes (to fit different bolt diameters)

• Drive sizes (the square opening that attaches to the ratchet)

• Point configurations (6-point, 12-point, etc.)

• Measurement systems (metric or SAE/imperial)

Why Do You Need a Socket Size Chart?

There are hundreds of fastener sizes, and guessing which socket you need wastes time and can damage your tools. A socket size chart works as a quick reference guide that matches bolt/nut sizes to their corresponding socket sizes.

For example:

• A 10mm bolt head requires a 10mm socket.

• A 1/2-inch nut requires a 1/2-inch socket.

With a chart, you can quickly look up the correct size instead of testing different sockets.

Metric vs. SAE Socket Sizes

Sockets mainly come in two measurement systems:

1. Metric (millimeters) – Common worldwide, especially in automotive and machinery applications.

   • Example sizes: 8mm, 10mm, 13mm, 17mm, 19mm, 21mm.

2. SAE (Society of Automotive Engineers, inches) – Standard in the U.S. for many construction and mechanical tools.

   • Example sizes: 1/4″, 3/8″, 7/16″, 1/2″, 9/16″.

👉 Pro tip: Sometimes, a metric socket is close enough to an SAE size and can fit (like 13mm vs. 1/2″). But it’s always best to use the exact match to avoid stripping the fastener.

Socket Drive Sizes

Apart from the diameter of the socket, another important factor is the drive size. This is the square opening that attaches to your ratchet handle. Common drive sizes include:

• 1/4-inch drive – Best for small fasteners and light-duty work.

• 3/8-inch drive – The most versatile, used for medium-sized bolts.

• 1/2-inch drive – Heavy-duty, great for automotive and machinery applications.

• 3/4-inch & 1-inch drive – For industrial or heavy equipment.

The drive size determines the strength and leverage you can apply. A socket size chart often lists which drive size works best with specific sockets.

Complete Socket Size Chart

Here’s a handy reference that combines metric and SAE socket sizes with their nearest equivalents.

Metric Socket Sizes (mm)

SAE (Imperial) Socket Sizes (inches)

Metric to SAE Conversion (Closest Matches)

Sometimes you don’t have the exact socket, so you can use a near-equivalent. Here are some useful matches:

• 8mm ≈ 5/16″

• 10mm ≈ 3/8″

• 11mm ≈ 7/16″

• 13mm ≈ 1/2″

• 14mm ≈ 9/16″

• 16mm ≈ 5/8″

• 19mm ≈ 3/4″

⚠️ Note: These are close but not identical. Use only in emergencies to avoid stripping.

Types of Sockets

Not all sockets are the same. Here are the main types:

1. Standard Depth Sockets – Everyday use for most bolts.

2. Deep Sockets – Useful for nuts on long bolts.

3. Impact Sockets – Designed for use with power tools, made of tougher steel.

4. Universal Joint Sockets – Swivel heads for reaching tight angles.

5. Spark Plug Sockets – Special sockets with rubber inserts for spark plugs.

How to Read and Use a Socket Size Chart

Using a socket size chart is simple:

1. Identify the fastener (nut or bolt) you need to tighten/loosen.

2. Measure the head size using calipers or a simple ruler.

3. Match it with the corresponding socket size from the chart.

4. Select the correct drive size based on the job’s torque requirements.

👉 Example: If you measure a bolt head at 13mm, you’ll need a 13mm socket, usually with a 3/8-inch drive for automotive tasks.

Common Mistakes to Avoid

• Mixing metric and SAE – Always use the right measurement system.

• Using too large a socket – This will round off the fastener edges.

• Forcing the wrong size – Can damage both the socket and the bolt.

• Ignoring drive size – A 1/4″ drive socket won’t fit a 1/2″ ratchet.

Tips for Choosing the Right Socket Set

1. Buy both metric and SAE – Covers all possible fasteners.

2. Go for quality – Cheap sockets crack under pressure.

3. Get a set with deep sockets – Invaluable for automotive work.

4. Keep them organized – Use labeled cases or socket rails.

5. Check compatibility – Ensure your ratchet matches the drive size.

Final Thoughts

A socket size chart is one of the most valuable references for anyone working with nuts and bolts. Whether you’re changing spark plugs, tightening a bike chain, or repairing heavy machinery, knowing the correct socket size saves time, prevents damage, and makes your work easier.

By understanding metric vs. SAE sizes, drive sizes, and socket types, you’ll be able to select the right tool every time. Keep this chart handy in your toolbox, and you’ll never waste time guessing again.

Also Read:

• Wrench Size Chart: Metric and SAE Sizes Guide (2025)